Omima S. Mohamed

Photocatalytic oxidation of selected aryl alcohols in acetonitrile

Abstract Photocatalytic oxidation of selected aryl alcohols ( 1 – 7 ) has been carried out by using anatase titanium dioxide catalyst. The main oxidation products were the corresponding aldehydes or ketones and acids, in addition to unidentified minor compounds. Kinetic studies revealed a second-order reaction rate for benzyl alcohol, as a model alcohol, photocatalytic oxidation. The suggested mechanism envisages electron–hole pair formation on the catalyst surface followed by oxidation–reduction reactions.

SYNTHESIS OF SOME NEW THIENO[2,3-b]PYRIDINES, PYRIDO[3′,2′:4,5]-THIENO[3,2-d]PYRIMIDINES AND PYRIDO[3′,2′:4,5]THIENO[3,2-d][1,2,3]-TRIAZINES

Abstract 4-Aryl-3-cyano-2-substituted-methyIthiocyclopenta[b]pyridines (3a-c and 4a-i) were prepared by reaction of 4-aryl-3-cyanocyclopenta[b]pyridine-2(1H)-thiones(2a-c) with chloroacetonitrile or chloro-N-arylacetamides, respectively. On treatment of these products with sodium ethoxide in boiling ethanol, they underwent intramolecular Thorpe-Ziegler cyclization to afford the corresponding 3-amino-4-aryl-2-functionallized-cyclopenta[e]thieno [2,3-b]pyridines (5a-c and 6a-i). Most of the latter thienopyridines were used as synthons for the target cyclopenta[5′,6′]pyrido[3′,2′:4.5]thieno[3,2-d]pyrimidines and cyclopenta[5′,6′]. pyrido[3′,2′:4,5]thieno[3,2-d][1,2,3]triazines.

SYNTHESIS AND REACTIONS OF SOME NEW HETEROCYCLIC COMPOUNDS CONTAINING THE THIENYLTHIENO[2,3-B]PYRIDINE MOIETY

(4-Aryl-3-cyano-6-(2-thienyl)pyridin-2-ylthio)acethydrazides (5a–c), 3-amino-4-aryl-6-(2-thienyl)thieno[2,3-b]pyridine-2-carbohydrazides (6a–c) and 3-amino-4-phenyl-6-(2-thienyl)thieno[2,3-b]pyridine-2-carboxylic acid (30) were prepared and employed as key intermediates in the synthesis of the title compounds.

Photocatalytic oxidation of selected fluorenols on TiO2 semiconductor

Abstract Photocatalytic oxidation of the title compounds 1 and 2 in nonaqueous oxygen saturated TiO 2 suspension was carried out. The corresponding ketones were formed in a high yield, in addition to minor amount of the corresponding hydrocarbon and other decomposition products. Interestingly, photocatalytic oxidation of the parent fluorene ( 3 ) afforeded fluorenone under the same conditions. Also, compound 4 as an acyclic simulant gave the corresponding ketone and hydrocarbon. Furthermore, the effect of solvent polarity has been tested. An electron–hole pair generated on the irradiated TiO 2 surface is suggested for the semiconductor-mediated photocatalysis.

TiO2 Nanoparticles-Photocatalytic Oxidation of Selected Cycloalkanols

Photocatalytic oxidation of cyclohexanol (1), cyclopentanol (2), and cycloheptanol (3) was investigated by using titanium dioxide (Degussa P25) as a semiconductor photocatalyst .The effect of different operational parameters such as the catalyst, the solvent, time, and oxidant was also studied. Results showed a high percentage of conversion for 1–3 (71.6%, 94.2%, and 100%, resp.) and that the primary photocatalytic oxidation products are the corresponding cycloalkanones (4–6). They were formed with high selectivity (>85%). Several other products were also identified using GC, GC/MS techniques and authentic samples. The photocatalytic activity is explained by a photoinduced electron transfer mechanism through the formation of electron-hole pair at the surface of the semiconductor particles. A first-order kinetic model was observed for the photocatalytic oxidation of the investigated cycloalkanols.

Studies on the Synthesis of Some New Cyanopyridine-Thione and Thieno[2,3-b]pyridine Derivatives

The work included in this article involves the synthesis of new cyanopyridinethiones as good synthons for new thieno[2,3-b]pyridines with anticipated biological activities. Thus, the reaction of β–aryl-α-thiocarbamoylacrylonitrile ( 1a–c ) with (2-thenoyl)-ω,ω,ω-trifluoroacetone led to an unexpected formation of 4-aryl-3-cyano-6-(2-thienyl)pyridine-2(1H)-thiones ( 4a–c ). In contrast, the reaction of 1a,b with ethyl acetoacetate produced 4-aryl-3-cyano-5-ethoxycarbonyl-6-methylpyridine-2(1H)-thiones ( 12a,b ). The reaction of compound 4a with methyl iodide gave 2-methylthio derivative 6 , which upon treatment with hydrazine hydrate furnished pyrazolopyridine 7 . Treatment of 4a–c with chloroacetaimde, in the presence of sodium ethoxide, led to the formation of 3-amino-4-aryl-6-(2-thienyl)thieno[2,3-b]pyridine-2-carboxamides ( 8a–c ). The reactions of 8a with some aromatic aldehydes and/or cycloalkanones were carried out and their products were identified. Compounds 12a,b were reacted with chloro-N-arylacetamides to give ethyl 4-aryl-2-(N-aryl)carbamoylmethylthio-3-cyano-6-methylpyridine-5-carboxylates ( 13a–j ). Upon treatment of compounds 13a–j with sodium alkoxide in alcohol, they underwent an intramolecular Thorpe-Ziegler cyclization to furnish ethyl 3-amino-4-aryl-2-(N-aryl)carbamoyl-6-methylthieno[2,3-b]pyridine-5-carboxylates ( 14a–j ). Compounds 14a–j , in turn, were reacted with triethyl orthoformate and/or carbon disulfide to give corresponding pyridothienopyrimidinone derivatives 15a–j and 18 . Pyridothienotriazinone analogs 17a–j were synthesized via diazotisation of compounds 14a–j .

Synthesis of some new pyridothienopyrimidines and related [1,2,4]triazolopyridothienopyrimidines

4-Chloro-9-phenyl-7-(2-thienyl)pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine (5) and 3-amino-3,4-dihydro-4-imino-9-phenyl-7-(2-thienyl)pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine (19) were prepared and employed as precursors for synthesizing the fused-ring compounds of the title.

Multiplicity and selectivity of cyclopent[a]acenaphthylenylidene

Abstract Cyclopent[a]acenaphthylenylidene 1 has been generated by photolysis from its precursor, the diazocompound 1a . Carbene 1 could be trapped in olefinic substrates to afford the spirocyclopropanes 8 – 12 . In addition triplet products of 1 such as 13 and dimer 14 were isolated. With trans-β-methylstyrene 1 undergoes a stereospecific addition. 2,3-Dimethylbutadiene and 1 reacted to the vinylspirocyclopropane 16 and 17 . Competition experiments of 1 with styrenes give a linear Hammett correlation with a ρ=0.38. Therefore, 1 is regarded as a nucleophilic singlet carbene in its additions to styrenes.